In vitro incubation of single nephron segments of rat kidney will be used to identify systemic factors that contribute to the increase in ammonia production observed in proximal tubules during metabolic acidosis. The relative contribution of factors such as pH, potassium concentration and adrenal hormones to the regulation of ammonia production will be examined. In a second series of experiments, rates of lactate production will be measured and compard among different nephron segments. These studies should provide important new information regarding the importance and regulation of glycolysis in defined portions of the nephron.